Known packaging apparatuses for packaging in bags a material in the form of liquid, powder, or particulate solid are typically such that each bag is first longitudinally supported, then opened at the mouth thereof, through which the material is filled into the bag. In packaging operations employing such apparatus, it is a usual practice that since the bags, being flexible and limp, cannot be placed upright in a bag loading box for housing the bags, the bags are stacked up in flat condition in the loading box so that they are picked up one by one, beginning with the uppermost one, each bag being longitudinally oriented in the course of transport thereof for being supplied to the packaging apparatus. U.S. Pat. No. 3,945,173 discloses an apparatus wherein bags placed flat on a stack are picked up one by one, beginning with the uppermost one, through suction by a suction cup, each bag so picked up being fed between a pair of clamps, which in turn engage the opposite sides of the bag adjacent the mouth thereof; then the mouth of the bag is opened by two suction cups and fitted around an outlet end of a hopper for filling a specified quantity of material into the bag as a pair of clamp arms rotate.
With the apparatus of U.S. Pat. No. 3,945,173, however, one difficulty is that when the bags piled up are picked up one by one through suction by the suction cup, it may occasionally happen that some bag is not properly picked up by the suction cup, because static electricity may occur among the bags. Another difficulty is that when a bag is being transported by the suction cup to the space between the pair of clamps, it may sometimes happen that the mouth of the bag becomes open to allow the entry of air thereinto, with the result of the bag dropping from the suction cup because the load of the bag becomes larger due to air resistance. In the latter mentioned case, if the bag does not drop from the suction cup, it may not be accurately clamped at opposite sides thereof near the bag mouth because the bag is fed and held in an incomplete position between the pair of clamps.
Another type of packaging apparatus is known, such as one disclosed in U.S. Pat. No. 4,027,456, wherein bags piled up in flat condition in a box are taken out one by one through roller movement, beginning with the lowermost bag, so that each bag is supplied between a pair of clamps. Such packaging apparatus has a difficulty that the lowermost bag in the box is subject to the influence of the load of many bags placed thereon and, therefore, that if the bags are of a thin and soft material, it is impracticable to take out one bag each against the friction resistance from and between individual bags thereon.
With any such prior art packaging apparatus as described above, therefore, some 2-4% packaging errors have been unavoidable if the bags to be filled were of a thin and flexible material.